When using the ? and :, it's a conditional operator, the same as using an if/else statement:

condition ? true result : false result

So to breakdown what your statement is doing, it first checks to see if DealStatus IS NULL. If so, it returns a "2". If it isn't NULL, it returns the first character of the DealStatus field using SUBSTRING. Finally, it compares that result to see if it's equal to "2".

The overall expression will return a true/false. For example, if DealStatus is NULL, this will always return true.

For example, here would be the results if the following values were stored in the DealStatus field.

DealStatus ResultOfCondition
NULL true (because DealStatus is NULL, we compare 2 == 2 is true)
123 false (because the first character is 1, 1 == 2 is false)
234 true (because the first character is 2, 2 == 2 is true)